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Better battery search keeps going and going


(NC&T/ASU) Chemists at ASU's Biodesign Institute have created a tiny hydrogen-gas generator that they say can be developed into a compact fuel cell package. This generator could then power portable electronic devices three to five times longer than conventional batteries of the same size and weight.

The generator uses a special solution containing borohydride, an alkaline compound that has an unusually high capacity for storing hydrogen, a key element that is used by fuel cells to generate electricity. In laboratory studies, prototype devices have been used to provide sustained power to light bulbs, a radio and a DVD player, the researchers say.

"We're trying to maximize the usable hydrogen storage capacity of borohydride to make the fuel cell power source last longer," says study leader Don Gervasio, who serves as an associate research professor within the institute's Center for Applied NanoBioscience. "That could lead to the most powerful power source ever produced for portable electronics."

The fuel cell system can be packaged in containers of the same size and weight as conventional batteries, and the system is recharged by refilling the fuel cartridge. Research on the battery replacement fuel cells, which also are safer for the environment, was described at the 232nd national meeting of the American Chemical Society.

Because higher hydrogen production translates into more energy for longer battery life, one of the challenges in fuel cell development is maximizing the concentration of hydrogen in the fuel source.

Many different hydrogen sources have been explored for use in fuel cells, including metal hydride "sponges" and hydrocarbons such as gasoline, methanol, ethanol and even vegetable oil.

Recently, borohydride has shown promise as a safe, energy-dense hydrogen storage solution. Unlike the other fuel sources, borohydride works at room temperature and does not require high temperatures to liberate hydrogen, Gervasio says.

The team at ASU is focused on a key enabling technology, the chemistry for developing useful fuels with higher energy density than battery metals.

Using novel chemical additives, Gervasio and his associates are working on a way to increase the useful hydrogen storage capacity of the borohydride solution two to three times the hydrogen capacity of simple aqueous sodium borohydride solutions that are being explored for fuel cell development.

These additives help to prevent the solution from solidifying, which could potentially clog or damage the hydrogen generator and cause it to fail.

In developing the prototype fuel cell system, the researchers housed the solution in a tiny generator containing a metal catalyst composed of ruthenium metal. In the presence of the catalyst, the borohydride in the water-based solution reacts to form hydrogen gas.

The hydrogen gas leaves the gas generator by moving across a special gas/liquid separating membrane to the fuel cell component, while the membrane retains the liquid in the catalytic gas generator. The hydrogen gas then combines with oxygen inside the fuel cell to generate water and electricity, which can be used to power a portable electronic device.

The byproduct of the reaction is a safe, nontoxic watery solution that remains trapped and secure in the fuel cell container.

Although the battery generates heat, it generally doesn't get any higher than body temperature, Gervasio says. And because the hydrogen generated by the device is matched by the rate of hydrogen consumption, there's virtually no free hydrogen gas during power generation, making the fuel cell safe, he says.

Although the fuel cell itself is reusable and doesn't need recharging, the borohydride fuel eventually is depleted. The fuel cell can be rejuvenated simply and quickly by adding a new cartridge of borohydride, Gervasio says.

While the prototype fuel cell is the size of a shoebox, it can easily be scaled down to the size and weight of a small, conventional battery, Gervasio says.

Commercialization could take as many as three to five years, so current technology users may need to put up with their regular batteries and rechargers for a while longer, he says.

Funding for this study was provided by the National Science Foundation through the Ira A. Fulton School of Engineering's Connection One program and by KITECH, the Korean Institute of Technology, a Korean national laboratory in Incheon, Korea.

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